Pattern forming method and photomasks used therefor

Abstract

In a photoresist pattern formation by exposure using first and second photomasks, the first photomask has a transparent part, a rectangular opaque part having a first pair of sides and a second pair of sides, and a phase shifter, having a first edge crossing one of the first pair of sides, so that a part of the first edge is in the transparent part, and the second photomask has a transparent part, a rectangular opaque part corresponding to the rectangular opaque part of the first photomask, and a stripe-shaped opaque part corresponding to the first part of the first edge of the phase shifter. The rectangular opaque part of the first photomask is expanded in the direction of the first pair of sides, while the rectangular opaque part of the second photomask is expanded in the direction the second pair of sides. The amount of expansion is preferably not smaller than a misalignment tolerance.

What is claimed is: 
     
       1. A method for forming patterns, comprising the steps of: preparing a first photomask having a first transparent part, a first rectangular opaque part having a first side and a second side perpendicular to the first side, and a phase shifter having a third side crossing the first side, the third side having a first part defined in the first rectangular transparent part, having a second part defined in the first rectangular opaque part and perpendicular to the first side;   preparing a second photomask having a second transparent part, a second rectangular opaque part corresponding to the first rectangular opaque part, and a stripe-shaped opaque part corresponding to the first part of the third side, having one end connected to the second rectangular opaque part and being wide enough to allow for misalignment between the first and second photomasks;   conducting a first exposure using the first photomask; and   conducting a second exposure using the second photomask before or after the first exposure;   wherein the first rectangular opaque part is expanded in the direction of the first side by an amount not smaller than a misalignment tolerance in the direction of the first side and is not expanded in the direction of the second side; and   the second rectangular opaque part is expanded in the direction of the second side by an amount not smaller than a misalignment tolerance in the direction of the first side.   
     
     
       2. Photomasks for use in a pattern formation comprising: a first photomask having a first transparent part, a first rectangular opaque part having a first side, and a second side perpendicular to the first side, and a phase shifter having a third side crossing the first side, the third side having a first part defined in the first transparent part, having a second part defined in the first rectangular opaque part and perpendicular to the first side; and   a second photomask having a second transparent part, a second rectangular opaque part corresponding to the first rectangular opaque part, and a stripe-shaped opaque part corresponding to the first part of the third side, having one end connected to the second rectangular opaque part and wide enough to allow for misalignment between the first and second photomasks;   wherein the first rectangular opaque part is expanded in the direction of the first side by an amount not smaller than a misalignment tolerance in the direction of the first side and is not expanded in the direction of the second side; and   wherein the second rectangular opaque part is expanded in the direction of the second side by an amount not smaller than a misalignment tolerance in the direction of the second side and is not expanded in the direction of the first side.